Such valve trains are basically known in the form of push rod valve trains in high-capacity internal combustion V-engines. Here the cam lifts of a camshaft supported in the engine block of the internal combustion engine in proximity to the crankshaft are first translated into a longitudinal movement of the valve tappets, which are likewise supported in the engine block and generally take the form of low-friction roller tappets. The reciprocating movement of the valve tappets is then transmitted by valve push rods, which actuate rocker arms supported in the cylinder head of the internal combustion engine, to the gas exchange valves associated with the valve tappets.
In such internal combustion engines a cylinder cut-off represents a highly effective measure for reducing the fuel consumption and in design terms is moreover particularly easy to implement. The requisite shutdown of the gas exchange valves of the cylinders cut off is achieved through the use of adjustable valve tappets having an outer part and an inner part, which can be coupled together as necessary by coupling means so as to permit a variable transmission of the cam lift to the valve push rod. Whilst the patent literature contains various proposals for the design of such valve tappets, a valve train regarded as generic and used in series production was demonstrated to experts at the 26th Vienna International Engine Symposium and documented in the “VDI Progress Reports”, volume series 12, No. 595. The valve tappet is in this case designed so that the inner part, displaceably supported in the longitudinal bore in the outer part, is forced by means of a lost-motion spring assembly arranged inside the longitudinal bore towards two superimposed retainer rings fixed in an annular groove of the outer part. In addition to their function as a device for securing the inner part during assembly and transport of the valve tappet, the retainer rings interacting with a stop face of the inner part serve, in a known manner, to ensure that the seats for the coupling means, running in the inner part and the outer part, always align with one another during the cam base circle phase.
As is also disclosed in some detail in DE 102 04 672 A1, two retainer rings, of which one is taken from a type assortment of retainer rings of variable thickness, are provided for ease of assembly in adjusting the closely toleranced coupling play between the coupling means and the seats. Such retainer rings for bores, which will also be known to the person skilled in the art under the trade name “Seeger ring”, have lugs separated by a fitting gap with fitting holes for a fitting tool. The lugs extending radially inwards on the inner circumference of the retainer ring mean that the clear space between the lugs and the valve push rod is significantly less than in the remaining area of the inner circumference. Since the valve push rod is generally fitted inclined in relation to the longitudinal axis of the valve tappet, however, and furthermore performs a swiveling movement superimposed on this inclination during operation of the internal combustion engine, the maintenance of the absolutely essential free movement between the valve push rod and the lugs of the retainer ring presents design problems. This applies, in particular, with regard to the valve tappet in the deactivated state, in which the inner part sinks into the outer part and the valve push rod is displaced in parallel in the direction of the retainer rings. In conjunction with unavoidable component tolerances, this interaction may lead to unwanted restrictions, particularly with regard to the diameter of the valve tappet and valve push rod, the inclination of the valve push rod and its operational swiveling range in relation to the longitudinal axis of the valve tappet and the height of the cam lift to be deactivated.
An interruptible valve tappet in which this problem does not occur is set forth in DE 102 12 522 A1. The retainer ring proposed therein, however, is a “Seeger ring” for shafts, which is fixed not in an inner annular groove of the outer part but in an outer annular groove of the inner part and which primarily serves to support a spring seating for the lost-motion spring, which runs around the inner part in the area of an end section of the valve tappet facing the valve push rod. In this respect the lugs of this retainer ring do not extend radially inwards on its inner circumference but radially outwards on its outer circumference. Consequently, with such a valve tappet there is also no risk of the valve push rod colliding with the lugs of the retainer ring.